Paleocene-Eocene Thermal Maximum (PETM)
- "The end of the Paleocene (~55 Ma) was marked by sudden global change,
upsetting oceanic and atmospheric circulation and leading to the
extinction of numerous deep-sea benthic foraminifera and a major turnover
in land mammals. Biotic and geochemical anomalies observed world-wide
relate to high latitude warming (subtropical conditions prevailed at
Antarctica!) and a reversal in oceanic circulation: during a short period
(<100 k.y.) dense warm and salty water, formed in low latitude basins
(e.g. Tethyan margins), is thought to have filled the oceanic basins.
This period is known as the Paleocene-Eocene Thermal Maximum, PETM
(previously known as LPTM, and also as IETM). Just over a decade ago the
abruptness of these events was first recognized. Today, this is regarded
as one of the most significant periods of global change during the
Cenozoic. Detailed study of these events could provide insight into
geobiosphere dynamics in an extreme greenhouse world."
The phrase "geobiosphere dynamics in an extreme greenhouse world" sounds
a lot like runaway GHG warming, do you agree?
What made warming from geobiosphere dynamics in an extreme greenhouse
world slow down 55 million years ago?
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- Discussion about PETM and on what killed the dinosaurs,
Evidence Of Global Warming In The Past Supports Greenhouse Theory
Santa Cruz - Oct 24, 2003
Scientists have filled in a key piece of the global climate picture for a
period 55 million years ago that is considered one of the most abrupt and
extreme episodes of global warming in Earth's history. The new results
from an analysis of sediment cores from the ocean floor are consistent
with theoretical predictions of how Earth's climate would respond to
rising concentrations of greenhouse gases in the atmosphere. The new
study, led by James Zachos, professor of Earth sciences at the University
of California, Santa Cruz, will be published online by Science Express on
October 23, and will appear in a later print edition of Science magazine.
The researchers analyzed sediments deposited on the seafloor during a
period known as the Paleocene-Eocene Thermal Maximum, when a massive
release of heat-trapping greenhouse gases is thought to have triggered a
runaway process of global warming. Climate theory predicts that the
increase in greenhouse gases would have caused temperatures to rise all
over the planet, with greater increases in sea surface temperatures at
high latitudes than at low latitudes.
Zachos and a team of researchers at UCSC and several other institutions
have now obtained the first reliable estimates of the change in tropical
sea surface temperatures during this period. When combined with existing
records of sea surface temperatures at high latitudes, the findings fit
well with the predictions of computer simulations based on current
The study provides important backing for the climate models that
scientists are using to predict the effects of the current rise in
atmospheric carbon dioxide due to industrial emissions, Zachos said.
"The predictions from the models seem to be consistent with the geologic
record, so I'd say greenhouse climate theory is alive and well," he said.
"People have raised questions about how accurate these models are in
terms of handling heat transport in response to rising greenhouse gases,
but this study indicates that the climate people have got it right or
close to right."
The Paleocene-Eocene Thermal Maximum, starting about 55 million years ago
and lasting about 150,000 years, is marked by dramatic changes in the
fossil record of life in the ocean and on land.
Average global temperatures increased by about 5 degrees Celsius (9
degrees Fahrenheit). The increase in sea surface temperatures at high
latitudes was 8 to 10 degrees Celsius, and the new study shows a 4- to
5-degree Celsius increase in tropical sea surface temperatures.
"This event is the best example of greenhouse warming in the geologic
record, and for the first time we have been able to document the climate
response on a relatively broad planetary scale, from the tropics to polar
latitudes," Zachos said.
The temperature estimates were derived from chemical analyses of the
shells of microscopic plankton preserved in the seafloor sediments. The
chemical composition of the plankton's calcite shells reflects the
temperature of the water in which they were formed. A key measurement
examined in this study was the ratio of magnesium to calcium, which
increases exponentially with the temperature at which the shells formed.
"The ratio of magnesium to calcium in seawater is relatively constant
over the timescale of this event, so the ratio in the shells is really
only sensitive to one variable, the calcification temperature," Zachos
UCSC graduate students Michael Wara and Steven Bohaty performed most of
the chemical analyses. The researchers analyzed sediment cores recovered
from a site called Shatsky Rise in the tropical Pacific during an
expedition of the ship JOIDES Resolution in 2001 (Leg 198 of the Ocean
Drilling Program). The cores provided a complete sequence of deposits
representing the boundary between the Paleocene and Eocene epochs.
"There aren't many places in the Pacific where you can recover sediments
of this age in which the fossils are not so recrystallized that they've
lost their original geochemical signatures," Zachos said.
ODP Leg 198 and a complementary drilling expedition in the Atlantic
earlier this year (ODP Leg 208) were designed to test the leading
explanation for the Paleocene-Eocene Thermal Maximum, which attributes it
to a massive release of methane. Methane, a potent greenhouse gas,
accumulates in frozen deposits known as clathrates found in the deep
ocean near continental margins and also in the Arctic tundra. For reasons
that remain unclear, the clathrates suddenly began to decompose,
releasing an estimated 2,000 gigatons (2 trillion tons) of methane.
Once released, the methane would have reacted with dissolved oxygen in
the ocean to produce carbon dioxide, another greenhouse gas. Large
amounts of both carbon dioxide and methane would have entered the
atmosphere, raising temperatures worldwide.
In addition to Zachos, Wara, and Bohaty, the coauthors on the Science
paper are Margaret Delaney, professor of ocean sciences at UCSC, Maria
Rose Petrizzo and Isabella Premoli-Silva of the University of Milan,
Amanda Brill of the University of North
Carolina, and Timothy Bralower of Pennsylvania State University.
Bralower and Premoli-Silva were co-chief scientists on ODP Leg 198.
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